The plasma instrumentation for the Galileo Mission

The plasma instrumentation (PLS) for the Galileo Mission comprises a nested set of four spherical-plate electrostatic analyzers and three miniature, magnetic mass spectrometers. The three-dimensional velocity distributions of positive ions and electrons, separately, are determined for the energy-per-unit charge (E/Q) range of 0.9 V to 52 kV. A large fraction of the 4-steradian solid angle for charged particle velocity vectors is sampled by means of the fan-shaped field-of-view of 160°, multiple sensors, and the rotation of the spacecraft spinning section. The fields-of-view of the three mass spectrometers are respectively directed perpendicular and nearly parallel and anti-parallel to the spin axis of the spacecraft. These mass spectrometers are used to identify the composition of the positive ion plasmas, e.g., H⁺, O⁺, Na⁺, and S⁺, in the Jovian magnetosphere. The energy range of these three mass spectrometers is dependent upon the species. The maximum temporal resolutions of the instrument for determining the energy (E/Q) spectra of charged particles and mass (M/Q) composition of positive ion plasmas are 0.5 s. Three-dimensional velocity distributions of electrons and positive ions require a minimum sampling time of 20 s, which is slightly longer than the spacecraft rotation period. The two instrument microprocessors provide the capability of inflight implementation of operational modes by ground-command that are tailored for specific plasma regimes, e.g., magnetosheath, plasma sheet, cold and hot tori, and satellite wakes, and that can be improved upon as acquired knowledge increases during the tour of the Jovian magnetosphere. Because the instrument is specifically designed for measurements in the environs of Jupiter with the advantages of previous surveys with the Voyager spacecraft, first determinations of many plasma phenomena can be expected. These observational objectives include field-aligned currents, three-dimensional ion bulk flows, pickup ions from the Galilean satellites, the spatial distribution of plasmas throughout most of the magnetosphere and including the magnetotail, and ion and electron flows to and from the Jovian ionosphere.     

Modelling Electrostatic Sheath Effects on Swarm Electric Field Instrument Measurements

The Electric Field Instrument (EFI) was designed to measure ionospheric ion flow velocities, temperatures and distribution functions at the ram face of the European Space Agency’s Swarm spacecraft. These flow velocities, combined with the known orbital velocity of the satellite and local magnetic field, will be used to infer local electric fields from the relation E=?v×B. EFI is among a class of many particle sensors and flow meters mounted on satellites to monitor in situ plasma conditions. The interpretation of the measurements made with EFI and similar sensors relies on a spacecraft sheath model. A common approach, valid in the relatively cold and dense ionospheric plasma, is to assume a potential drop in a thin sheath through which particle deflection and energisation can be calculated analytically. In such models, sheath effects only depend on the spacecraft floating potential, and on the angle of incidence of particles with respect to the normal to the surface. Corrections to measurements are therefore local as they do not depend on the geometry of nearby objects. In an actual plasma, satellites are surrounded by electrostatic sheaths with a finite thickness. As a result, local corrections to particle distribution functions can only be seen as an approximation. A correct interpretation of measured particle fluxes or particle distribution functions must, at least in principle, account for the extent and shape of the sheath in the vicinity of the measuring instrument. This in turn requires a careful analysis of the interaction of the satellite with the surrounding plasma, while accounting for detailed aspects of the geometry, as well as for several physical effects. In this paper, the validity of the thin sheath model is tested by comparing its predictions with detailed PIC (Particle In Cell) calculations of satellite-plasma interaction. Deviations attributed to sheath finite thickness effects are calculated for EFI measurements, with representative plasma parameters encountered along the planned Swarm orbit. Finite thickness effects of the plasma sheaths are found to induce EFI velocity measurement errors not exceeding 37 m/s, with larger errors occurring in plasmas that are simultaneously tenuous (10⁹ m^?3 or lower) and warm (0.5 eV or higher).     

Satellite measurements of high latitude convection electric fields

This paper reviews the first results of satellite experiments to measure magnetospheric convection electric fields using the double-probe technique.The earliest successful measurements were made with the low-altitude (680–2530 km) polar orbiting Injun-5 spacecraft (launched August, 1968). The Injun-5 data are discussed in detail. The Injun-5 results are compared with the initial findings of the electric field experiment on the polar orbiting OGO-6 satellite (400–1100 km, launched June, 1969).In addition to electric fields, the Injun-5 spacecraft also measures electric antenna impedance and thermal and energetic charged particle densities. Knowledge of these parameters makes possible a detailed investigation of the operation of the electric antenna system. We report on this investigation and discuss errors attributed to sunlight shadows on the probes, wake effects, and other factors. The Injun-5 experiment can generally determine electric fields to an accuracy of about ±30 mV m^-1, and under favorable conditions, accuracies of ±10 mV m^-1 can be obtained.Reversals in the electric field at auroral zone latitudes are the most significant convection electric field effect discovered in the Injun-5 data. Electric field magnitudes of typically 30 mV m^-1, and sometimes 100 mV m^-1, are associated with reversals. Electric field reversals occur on 36% of auroral zone traversals, at about 70° to 80° invariant latitude, at all local times, and in both hemispheres. The latitude of a reversal often changes markedly on time scales less than 2 h. Electric potentials of greater than 40 keV are associated with these high latitude electric fields. Reversals occur at the boundary of measurable intensities of >45 keV electrons and are coincident with inverted V type low energy electron precipitation events. In almost all cases the E×B/B ² plasma convection velocities associated with reversals are directed east or west, with anti-sunward components at higher latitudes and sunward components at lower latitudes. Maximum convection velocities are typically 1.5 km s^-1 and ordinarily occur at the auroral zone near the reversal.Two extreme (and many intermediate) configurations of anti-sunward plasma convection have been observed to occur on the high latitude side of electric field reversals: (1) Ordinarily, >0.75 kms^-1 convection is limited to narrow (5° INV wide) zones adjacent to the reversal. (2) For 14% of reversals >0.75 km s^-1 anti-sunward convection has been observed across the entire polar cap along the trajectory of the Injun-5 spacecraft. A summary pattern of >0.75 km s^-1 polar thermal plasma convection is presented.Electric field measurements from the OGO-6 satellite have substantiated many of the initial Injun-5 observations with improved accuracy and sensitivity. The OGO-6 detector revealed the persistent occurrence of anti-sunward convection across the polar cap region at velocities (<0.75 km s^-1) not generally detectable with the Injun-5 experiment. The OGO-6 observations also provided information indicating that the location of the electric field reversal shifts equatorward during periods of increased magnetic activity.The implications of the electric field measurements for magnetosphericand auroral structure are summarized, and a list of specific recommendations for improving future experiments is presented.     

An Overview of the Fast Auroral SnapshoT (FAST) Satellite

The FAST satellite is a highly sophisticated scientific satellite designed to carry out in situ measurements of acceleration physics and related plasma processes associated with the Earth's aurora. Initiated and conceptualized by scientists at the University of California at Berkeley, this satellite is the second of NASA's Small Explorer Satellite program designed to carry out small, highly focused, scientific investigations. FAST was launched on August 21, 1996 into a high inclination (83°) elliptical orbit with apogee and perigee altitudes of 4175 km and 350 km, respectively. The spacecraft design was tailored to take high-resolution data samples (or `snapshots') only while it crosses the auroral zones, which are latitudinally narrow sectors that encircle the polar regions of the Earth. The scientific instruments include energetic electron and ion electrostatic analyzers, an energetic ion instrument that distinguishes ion mass, and vector DC and wave electric and magnetic field instruments. A state-of-the-art flight computer (or instrument data processing unit) includes programmable processors that trigger the burst data collection when interesting physical phenomena are encountered and stores these data in a 1 Gbit solid-state memory for telemetry to the Earth at later times. The spacecraft incorporates a light, efficient, and highly innovative design, which blends proven sub-system concepts with the overall scientific instrument and mission requirements. The result is a new breed of space physics mission that gathers unprecedented fields and particles observations that are continuous and uninterrupted by spin effects. In this and other ways, the FAST mission represents a dramatic advance over previous auroral satellites. This paper describes the overall FAST mission, including a discussion of the spacecraft design parameters and philosophy, the FAST orbit, instrument and data acquisition systems, and mission operations.     

Field-aligned (Birkeland) currents

Following earlier suggestions of Edmond Halley and Anders Celsius for the magnetic behavior of auroral phenomena, Kristian Birkeland discovered in his polar expeditions of 1902–03 that large-scale electric currents were associated with the aurora. He was also the first to suggest that these currents originated far from earth and that they flowed into the upper polar atmosphere and out of it along magnetic field lines; the existence of such field-aligned currents was widely disputed until satellite and rocket-borne instruments confirmed their permanent existence. The importance of these Birkeland currents to the coupling between the magnetosphere and the polar ionosphere is emphasized by their intensity, which ranges between 10⁶ and 10⁷ amperes, and by the energy which they dissipate in the upper atmosphere, which can exceed by a considerable factor the energy dissipated there by auroral particles. The large- and small-scale average properties of field-aligned currents, determined from spacecraft observations, are reviewed here.     

The Magnetostatic Cleanliness Program for the Cassini Spacecraft

The Cassini spacecraft, launched in October 1997 and expected to reach Saturn in 2004, carries two magnetometer experiments on a 10-m boom, one at the mid-section of the boom and the other situated at the end of the boom. In order to gather valid scientific magnetic field data and avoid electromagnetic interference, the spacecraft had to comply with stringent magnetostatic cleanliness requirements. This paper describes the results of the Cassini magnetics cleanliness program that achieved the goal of minimizing the magnetic field interference with Cassini’s DC magnetic field science instruments.     

The Magnetostatic Cleanliness Program for the Cassini Spacecraft

The Cassini spacecraft, launched in October 1997 and expected to reach Saturn in 2004, carries two magnetometer experiments on a 10-m boom, one at the mid-section of the boom and the other situated at the end of the boom. In order to gather valid scientific magnetic field data and avoid electromagnetic interference, the spacecraft had to comply with stringent magnetostatic cleanliness requirements. This paper describes the results of the Cassini magnetics cleanliness program that achieved the goal of minimizing the magnetic field interference with Cassini’s DC magnetic field science instruments.This revised version was published online in July 2005 with a corrected cover date.     

The Electric Field Instrument (EFI) for THEMIS

The design, performance, and on-orbit operation of the three-axis electric field instrument (EFI) for the NASA THEMIS mission is described. The 20 radial wire boom and 10 axial stacer boom antenna systems making up the EFI sensors on the five THEMIS spacecraft, along with their supporting electronics have been deployed and are operating successfully on-orbit without any mechanical or electrical failures since early 2007. The EFI provides for waveform and spectral three-axis measurements of the ambient electric field from DC up to 8 kHz, with a single, integral broadband channel extending up to 400 kHz. Individual sensor potentials are also measured, providing for on-board and ground-based estimation of spacecraft floating potential and high-resolution plasma density measurements. Individual antenna baselines are 50- and 40-m in the spin plane, and 6.9-m along the spin axis. The EFI has provided for critical observations supporting a clear and definitive understanding of the electrodynamics of both the boundaries of the terrestrial magnetosphere, as well as internal processes, such as relativistic particle acceleration and substorm dynamics. Such multi-point electric field observations are key for pushing forward the understanding of electrodynamics in space, in that without high-quality estimates of the electric field, the underlying electromagnetic processes involved in current sheets, reconnection, and wave-particle interactions may only be inferred, rather than measured, quantified, and used to discriminate between competing hypotheses regarding those processes.     

主被动复合驱动空间探测柔性伸杆机构的参数匹配

基于主被动复合驱动的思想提出一种大伸展/收拢比、高载荷/自重比的新型伸缩式伸杆机构,以满足微纳探测器的实际应用需求,用于支撑各类探测载荷远离航天器本体,避免本体剩磁对空间待测信号的干扰,保证探测数据的准确性。首先,探索描述被动驱动源（弹簧铰链）的力矩驱动特性;然后,分析柔性伸杆的弯曲、扭转、压平和卷曲等力学性能。在此基础上,结合建立的柔性伸杆伸展速度、负载动能、弹簧铰链势能及主动驱动（电动机）力矩等参数的能量流约束方程,进行主、被动驱动和柔性伸杆的参数匹配研究;最后,利用有限元软件仿真和样机平台实验验证了参数匹配的合理性。仿真与实验结果表明,针对主被动复合驱动的空间探测柔性伸杆机构,通过合理的参数匹配,可实现柔性伸杆无褶皱地平稳伸展和收拢,为后续的机构设计和控制方案奠定了基础。     

主被动复合驱动空间探测柔性伸杆机构的参数匹配简

 基于主被动复合驱动的思想提出一种大伸展/收拢比、高载荷/自重比的新型伸缩式伸杆机构,以满足微纳探测器的实际应用需求,用于支撑各类探测载荷远离航天器本体,避免本体剩磁对空间待测信号的干扰,保证探测数据的准确性。首先,探索描述被动驱动源（弹簧铰链）的力矩驱动特性;然后,分析柔性伸杆的弯曲、扭转、压平和卷曲等力学性能。在此基础上,结合建立的柔性伸杆伸展速度、负载动能、弹簧铰链势能及主动驱动（电动机）力矩等参数的能量流约束方程,进行主、被动驱动和柔性伸杆的参数匹配研究;最后,利用有限元软件仿真和样机平台实验验证了参数匹配的合理性。仿真与实验结果表明,针对主被动复合驱动的空间探测柔性伸杆机构,通过合理的参数匹配,可实现柔性伸杆无褶皱地平稳伸展和收拢,为后续的机构设计和控制方案奠定了基础。     

The Freja F3C Cold Plasma Analyzer

The F3C Cold Plasma Analyzer (CPA) instrument on theFreja spacecraft is designed to measure the energy per unit charge (E/Q) of ions oe electrons in the range 0<E/Q<200 V and complements the observations made by the F3H Hot Plasma Experiment. The CPA sensor, which is deployed on a boom, is an electrostatic analyzer which produces angle/energy images of particles incident on the sensor in a plane perpendicular to the boom axis. Charged particles incident normal to the CPA sensor housing axis of symmetry, which coincides with the boom axis, pass through collimators and enter a semi-spherical electrostatic analyzer which disperses particles in energy and azimuthal angle of arrival onto an imaging MCP detector thus producing images of the particle distributions in a plane perpendicular to the boom axis. Measurements are transmitted either as discrete 16×16 (angle/energy) images or as parameters related to the incident particle distribution function. Pixels in the discrete images are separated approximately equally in azimuthal angle while the 16 energy bins are separated approximately geometrically in energy. The ratio of the maximum to minimum energy imaged is programmable up to a maximum of more than a factor of ten, and the energy range itself is also under the control of the processor and can be varied by more than an order of magnitude. The density dynamic range of the sensor is increased by the introduction of an electrostatic gating system between the entrance aperture and the analyzer which can be used to duty-cycle low-energy electrons into the sensor thus keeping the count rate within appropriate levels. To reduce the effects of spacecraft induced perturbations on the lower-energy particle distributions, the sensor portion of the instrument is deployed on a 2 m long boom, perpendicular to the spacecraft spin axis. Spacecraft rotation is used to recover complete (4) angle/energy distributions every half spin period. In addition, the sensor skin may be biased with respect to the spacecraft ground to offset effects due to spacecraft charging. Current to the skin is monitored, making the exterior of the sensor equivalent to a large cylindrical Langmuir probe. Two separate processing paths for signals from the MCP anode may be chosen; slow and rast. The slow pulse processing path provides discrete angle/energy images at a nominal rate of 10 images per second and a peak burst mode rate of 100 images per second. The fast analog or current mode path provides crude parameterized estimates of densities, temperatures and drift velocities at nominal rates of up to 1000 parameters per second with a burst rate near 6000 parameters per second. Observations of cold ions and electrons in an unperturbed ionospheric plasma are presented which demonstrate the functionality of the instrument. Suprathermal ion observations in a transverse ion energization or acceleration region are also shown which demonstrate many of the small-scale features of these events.The Canadian Government's right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledge.     

The FAST Satellite Fields Instrument

We describe the electric field sensors and electric and magnetic field signal processing on the FAST (Fast Auroral SnapshoT) satellite. The FAST satellite was designed to make high time resolution observations of particles and electromagnetic fields in the auroral zone to study small-scale plasma interactions in the auroral acceleration region. The DC and AC electric fields are measured with three-axis dipole antennas with 56 m, 8 m, and 5 m baselines. A three-axis flux-gate magnetometer measures the DC magnetic field and a three-axis search coil measures the AC magnetic field. A central signal processing system receives all signals from the electric and magnetic field sensors. Spectral coverage is from DC to 4 MHz. There are several types of processed data. Survey data are continuous over the auroral zone and have full-orbit coverage for fluxgate magnetometer data. Burst data include a few minutes of a selected region of the auroral zone at the highest time resolution. A subset of the burst data, high speed burst memory data, are waveform data at 2×10⁶ sample s^–1. Electric field and magnetic field data are primarily waveforms and power spectral density as a function of frequency and time. There are also various types of focused data processing, including cross-spectral analysis, fine-frequency plasma wave tracking, high-frequency polarity measurement, and wave-particle correlations.     

RPC-MAG The Fluxgate Magnetometer in the ROSETTA Plasma Consortium

The fluxgate magnetometer experiment onboard the ROSETTA spacecraft aims to measure the magnetic field in the interaction region of the solar wind plasma with comet 67P/Churyumov-Gerasimenko. It consists of a system of two ultra light (about 28 g each ) triaxial fluxgate magnetometer sensors, mounted on the 1.5 m long spacecraft boom. The measurement range of each sensor is ±16384 nT with quantization steps of 31 pT. The magnetometer sensors are operated with a time resolution of up to 0.05 s, corresponding to a bandwidth of 0–10 Hz. This performance of the RPC-MAG sensors allows detailed analyses of magnetic field variations in the cometary environment. RPC-MAG furthermore is designed to study possible remnant magnetic fields of the nucleus, measurements which will be done in close cooperation with the ROSETTA lander magnetometer experiment ROMAP.     

The plasma mantle: Composition and other characteristics observed by means of the PROGNOZ-7 satellite

A brief summary of the main results of magnetospheric ion composition measurements in general is first presented. PROGNOZ-7 measurements in the nightside plasma mantle are then described and analyzed. Some of the results are the following: In the nightside mantle not too far from midnight the properties of the mantle are sometimes consistent with the open magnetosphere model. However during most magnetic storm situations O⁺ ions appear in the mantle in large proportions and with high energies. The acceleration process affecting the ions has been found in several cases to give equal amounts of energy to all ions independent of mass. Along the flanks of the magnetosphere the flow of the plasma is often low or absent. The O⁺ content is high (up to 20%) and the energy spectrum of both ions and electrons may be very hot, even up to the level of the ring current plasma in the keV range.The O⁺ content in the plasma mantle is positively correlated with the magnetospheric activity level. The mantle, however, does not appear to be the dominating source for the storm time ring current. Direct acceleration of ionospheric ions onto the closed field lines of the plasma sheet and ring current is most likely the main source. The magnetopause on the nightside and along the flanks of the magnetosphere appears to be a fairly solid boundary for mantle ions of ionospheric origin. This is especially evident during periods with high geomagnetic activity, when the mantle is associated with fairly strong fluxes of O⁺ ions.An interesting observation in most of the mantle passages during geomagnetically disturbed periods is the occurrence of intense, magnetosheath like, regions deep inside the mantle. In some cases these regions with strong antisunward flow and with predominant magnetosheath ion composition was observed in the innermost part of the mantle, i.e. marking a boundary region between the lobe and the mantle. These magnetosheath penetration events are usually associated with strong fluxes of accelerated ionospheric ions in nearby parts of the mantle. Evanescent penetration regions with much reduced flow properties are frequently observed in the flank mantle.     

离子发动机羽流特性的数值模拟

离子发动机羽流中产生的交换电荷(CEX)离子返流会影响航天器的正常工作.建立离子发动机羽流模型,采用单元内粒子方法(PIC)对羽流场进行数值模拟计算.结合DS-1探测器飞行实验的测量结果,分析了卫星电势、电子温度、卫星几何尺寸、推力器工作特性等对相关因素对CEX离子返流特性的影响.结果表明:从推力器出口附近到卫星背面,CEX离子密度为108~1012m-3.当卫星电势从-15V变化到27V,测量点位置处CEX离子密度从0.65×1012m-3变化到1.5×1012m-3.羽流中CEX离子密度和电势结构随电子温度变化不大,但电势大小随电子温度成比例地变化.同一位置处不同工况下CEX离子的密度可根据CEX离子生成率与工作点参数间的关系式准确地估计.卫星安装推力器的表面起着对CEX离子返流屏蔽和降低的作用.      

Quantitative models of the magnetospheric magnetic field: Methods and results

The paper reviews various approaches to the problem of evaluation and numerical representation of the magnetic field distributions produced within the magnetosphere by the main electric current systems including internal Earth's sources, the magnetopause surface current, the tail plasma sheet, the large-scale systems of Birkeland current, the currents due to radiation belt particles, and the partial ring current circuit. Some basic physical principles as well as mathematical background for development of magnetospheric magnetic field models are discussed.A special emphasis is placed on empirical modeling based on datasets created from large bodies of spacecraft measurements. A review of model results on the average magnetospheric configurations and their dependence on the geomagnetic disturbance level and the state of interplanetary medium is given. Possibilities and perspectives for elaborating the instantaneous models capable of evaluating a current distribution of magnetic field and force line configuration based on a synoptic monitoring the intensity of the main magnetospheric electric current systems are also discussed. Some areas of practical use of magnetospheric models are reviewed in short. Magnetospheric plasma and energetic particle measurements are considered in the context of their use as an independent tool for testing and correcting the magnetic field models.     

Studies of anomalous potential drops due to ion density inhomogeneities

The dynamic response of a 1-dimensional plasma diode to an applied step voltage is studied during a few electron transit times by numerical simulations when the initial state has an ion density minimum (an ion density cavity). Depending on the cavity depth and the applied voltage the potential drop distributes over the cavity or concentrates in a cathode sheath. The transistion between the two states as well as the cavity potential profiles are predicted by an analytical model. Simulations with periodic cavities as initial state show that the applied voltage can be shared between the cavities. A double layer, steady on the ion time scale, is created by introducing a steady cavity by ion losses.     

The electric field instrument on the polar satellite

The Polar satellite carries a system of four wire booms in the spacecraft spin plane and two rigid booms along the spin axis. Each of the booms has a spherical sensor at its tip along with nearby guard and stub surfaces whose potentials relative to that of their sphere are controlled by associated electronics. The potential differences between opposite sphere pairs are measured to yield the three components of the DC to >1 MHz electric field. Spheres can also be operated in a mode in which their collected current is measured to give information on the plasma density and its fluctuations. The scientific studies to be performed by this experiment as well as the mechanical and electrical properties of the detector system are described.     

Finite Larmor radius effects in the magnetosphere

This article reviews theories and observations related to effects produced by finite (and large) Larmor radii of charged particles in the magnetosphere. The FLR effects depend on =r _H /L, wherer _H is the Larmor radius andL is the spatial scale for field/plasma inhomogeneity. The parameter is a basic expansion parameter for most equations describing plasma dynamics in the magnetosphere. The FLR effects enter naturally the drift approximation for particle motion and represent also non-ideal MHD terms in the fluid formalism. The linear and higher order terms in lead to charge separation, energization of particles, and produce viscosity without collisions. The FLR effects introduce also important corrections to the dispersion relations for MHD waves and drift instabilities. Expansion of plasma into magnetic field leads to filamentation of the plasma boundary and to creation of structures with thickness less than an ion gyroradius. Large Larmor radius effects (1) in curved magnetic field geometry lead to stochastic behaviour of particle trajectories and to deterministic chaos. The tiny scale of the electron and ion gyroradii does not necessarily mean that FLR/LLR phenomena have negligible effect on the macroscopic dynamics and energetics of the whole magnetosphere. On the contrary, the small scale gyro-effects may provide the physical mechanism for gyroviscous coupling between the solar wind and the magnetosphere, the mechanism for triggering disruption of the magnetotail current layer, and the mechanism for parallel electric field that accelerate auroral particles.     

Early results from ISEE-1 electric field measurements

The double probe, floating potential instrumentation on ISEE-1 is producing reliable direct measurements of the ambient DC electric field at the bow shock, at the magnetopause, and throughout the magnetosheath, tail plasma sheet and plasmasphere. In the solar wind and in middle latitude regions of the magnetosphere spacecraft sheath fields obscure the ambient field under low plasma flux conditions such that valid measurements are confined to periods of moderately intense flux. Initial results show: (a) that the DC electric field is enhanced by roughly a factor of two in a narrow region at the front, increasing B, edge of the bow shock, (b) that scale lengths for large changes in E at the sub-solar magnetopause are considerably shorter than scale lengths associated with the magnetic structure of the magnetopause, and (c) that the transverse distribution of B-aligned E-fields between the outer magnetosphere and ionospheric levels must be highly complex to account for the random turbulent appearance of the magnetospheric fields and the lack of corresponding time-space variations at ionospheric levels. Spike-like, non-oscillatory, fields lasting <0.2 s are occasionally seen at the bow shock and at the magnetopause and also intermittently appear in magnetosheath and plasma sheet regions under highly variable field conditions. These suggest the existence of field phenomena occurring over dimensions comparable to the probe separation and c/_pe (the characteristic electron cyclotron radius) where _pe is the electron plasma frequency.